The projects under study are designed to give an understanding of the manner in which vascular endothelium may produce regulatory factors influencing granulopoiesis, megakaryocytpoiesis and erythroid development. The role of vascular endothelium is being studied, utilizing short term human and porcine endothelial cell cultures. We are presently establishing the utility of the porcine system for the production of these factors and, in particular, the ability of endothelium to support long-term porcine marrow culture growth. We have recent negative evidence with regard to the ability of this tissue to produce erythropoietin, but are currently investigating the possibility that intermediary regulator cells, in particular, monocytes or granulocytes, may produce monokines or granulokines, which then stimulate the endothelium to make hematopoietic regulatory factors. Establishment of the porcine system in which long-term reproducible growth of porcine endothelial cells is easily obtained has been established as a priority before initiating studies on the biochemical characterization of these factors. Overall, the endothelium remains an exciting potential regulator tissue with regard to hematopoietic proliferation and differentiation, and this remains the main thrust of our studies.